This invention relates to an improvement in a continuous process for the chlorination of butadiene to a mixture of dichlorobutenes.
Dichlorobutenes are important intermediates in the synthesis of chloroprene, which is the key monomer in the manufacture of neoprene rubbers as well as of hexamethylenediamine, which is one of the starting materials in the synthesis of nylon 66 polyamides.
Vapor phase chlorination of butadiene to dichlorobutenes is well known. One commercial process is described in British Pat. No. 1,290,607 to E. I. du Pont de Nemours and Company. This process is carried out under substantially adiabatic conditions in a tubular reactor. Butadiene and chlorine vapor are combined in a molar ratio of about 5:1 to 50:1 (preferably, 8:1 to 30:1) at a temperature of about 70.degree.-175.degree. C. and introduced into a reactor maintained at a temperature below 250.degree. C. The product stream contains dichlorobutenes, butadiene, trichlorobutenes and tetrachlorobutanes. This process is capable of giving high yields of dichlorobutenes, usually in excess of 90%, normally about 91-93%.
Because of the large scale of industrial operations in which dichlorobutenes are produced, there is a considerable economic incentive in improving the yields of dichlorobutenes still further; or, in the alternative, in increasing the reactor capacity without a loss of yield. Mere increase of the feed rates results in a yield loss.